In a part of our program concerned with the isolation and identification of unusual nucleic acid components, we have isolated several compounds from the urines of cancer patients. Preliminary work on five of these substances, designated as unknowns S,T,U,V and W, indicates that these compounds are related to the unusual nucleosides and bases of tRNA. In addition to these studies, we have isolated two compounds present in the urines of colon carcinoma patients. The unknown W and the latter two substances have not been detected in the urines of normal subjects. Since the levels of some of the modified nucleosides are elevated in the urines of leukemia and cancer patients as compared to the normals, our program seeks to determine the potential of the urinary nucleosides as the possible indicators (markers) of neoplastic activity in man. From this standpoint, we hope to estimate the urinary levels of the previously identified nucleosides, N-(purin-6-ylcarbamoyl)-L-threonine riboside (t6A), N6-methyladenosine, 2'-O-methylcytidine, 1-methylinosine and N3-methyluridine in the urines of patients with gastro-intestinal carcinoma, breast carcinoma and soft tissue sarcoma. The levels of the above nucleosides will be measured by the gas-liquid chromatography technique. For facile isolation of the unknown nucleosides from urine, the methods based on the interaction with the cis-diol grouping of ribose will be explored. Particularly the complexing of the cis-hydroxyls to borate containing column supports and the 2'3-isopropylidene type of derivativation of the urinary nucleosides will be tried. On the whole, this program should provide the structures of new urinary purine or pyrimidine derivatives, originally present in human tumor tRNA. The quantitative estimation of the above nucleosides in the urines of cancer patients may lead to the use of these substances as indicators of tumor activity in man.